Semiconductor devices, such as integrated circuits or microcircuits, are widely used in modern electronic applications. Often, semiconductor devices generate relatively high amounts of heat due to the current passing through various devices and circuits within the semiconductor devices. For example, in power-supply applications and Radio Frequency (RF) applications, semiconductor devices can pass a larger amount of current or operate at higher frequencies (often with frequencies in the multiple gigahertz), both of which result in a higher heat load. If this heat is not dissipated from the die, the semiconductor device can begin to experience errors and/or failure. With adequate heat dissipation, semiconductor devices can often operate with a higher current load, higher operating frequency, and, potentially, a longer anticipated lifespan. Thus, optimal heat dissipation is often a concern in the design and packaging of semiconductor devices, as well as the design of the actual integrated circuit die.
Presently, it is common to couple an integrated circuit die to one or more thermal layers, flanges, or structures within the device packaging of a semiconductor device. This thermal layer, flange, or structure dissipates heat away from the integrated circuit die (the primary source of the heat) toward surrounding air or another thermally-coupled structure (for example, a dedicated heat-sink or a frame or chassis of a larger device into which the semiconductor device is integrated). The thermal conductivity of the material used to construct the thermal layer has a direct impact on the ability of the thermal layer to dissipate the heat. For example, a material with a higher thermal conductivity may be better suited to communicate heat away from the integrated circuit die than would a material with a lower thermal conductivity.
However, there are other often competing concerns or factors to consider when selecting the material used for a thermal layer, flange, or structure (or of other portions of a semiconductor device). One such factor is the coefficient of thermal expansion (CTE) of the respective materials used within a semiconductor device. CTE represents the physical amount of expansion or contraction a material will experience as the material heats up or cools down, respectively. More particularly, a factor in the design of semiconductor devices is the variance of CTEs amongst various materials used within a semiconductor device. A greater disparity in CTEs of coupled materials can result in greater physical stresses within the semiconductor device particularly as it heats up. The stresses are the result of one material physically expanding more than another material, which stresses can cause joints to break or materials to crack.